Rotary dewatering sieve



Julyzs, 1931.-

J. STRINDLUND ROTARY DEWATERING SIEVE f Filed Jan. 5, 1930 Patented July 28,` 1931 'JOHN` STRINDL'UND, OIE HUBM, NORWAY ROTARY DEWATEBING SIEVE Application led January 3, 1980, vSerial Noi 418,316, 'and in Norway June 11, 1929.

This invention relates to dewatering sieves for cellulose and the like of the kind in which a sieve cylinder rotates partially immersed in a pulp mixture which surrounds the cylinder,

5 the pulp following the sieve out of the mixture and being removed from it at the top part of the sieve and the water leaving the cylinder through one or both ends thereof.

y In these known constructionsthe dewatering l is-based on the difference, in pressure, which is produced through the level of the outflowing Water inside .the sieve being lower than the level of the pulp mixture outside it. rI he diii'erence in pressure is, however, greatest at l the lower part of the sieve and decreases as the layer of pulp approaches the level of the pulp mixture, where it becomes zero. Consequently the pulp layer tends to become detached from the sieve and has diiiiculty in following it upwards out of the pulp mixture,

adhesion only being possible on the uppermost part of the sieve.

The disadvantage is overcome by the present invention according to the main characteristic feature of whichV the difference in pressure referred to is maintained until the pulp layer has passed above the level of the pulp mixture, after which it may even increase. lo One constructional form of the invention is illhulstrated in the accompanying drawings in w 'ch Y Fig. 1 is a section through a cylindrical' sieve in accordance with the invention and Fig. 2 shows diagrammatically an arrangement in which the layer of pulp is taken' off the sieve by means of an endless felt cloth. 1 is a cylindrical sieve which' rotates while partly immersed in a trough 2 to which the pulp mixture is conveyed by overflowing from from a chamber 3. The sieve is divided at its periphery into a number ofchambers or cells 4 which are covered on the outside by the sieve cloth or the covering 5. Each of the said cells communicates with one or more outflow pipes or passages 6 which are bent backwards with respect to the direction of ro tation of the sieve and the length of which is such that the outiiow end of the pipes does vnot rise out ofthe water in the interior of the sieve before the cellcommunicating with the pipe or pipes has passed above the level of the pulp mixture and has a proached the means or removing the pulp or instance the Aremoving roller 7 with the scraper 8 shown 55 in Fig. 1. 9 and 10 are two dandy. rollers. In Fig. 2'the scraper is replaced by an endless felt cloth 11 which is guided over guide rollers 12 and a removing roller 13 and which carries the web of pulp with it and leads it away to the outside between pressing rollers 14.

AWhen the cylindrical sieve rotates in the direction indicated by the arrow a layer will form on the sieve cloth as soon as the latter enters the pulp mixture, owing to the diierence in pressure produced between the liquid level outside the drum and inside the cell.

This diiierence in pressure increases as the sieve cloth proceeds through the pulp mixture andthe water which is separated off passes into the cells and into the pipes communicating with them, llin them entirely or par tially according to t e water content in the pulp mixture and the volume of the cells and '35 the pipes. When'the cells and the pipes are not completely filled b the water penetrating through the sieve clot the remamder of the filling will take place through the outflow end of the pipe at the moment in which the end 0 moves below.the water level in the interior of the cylinder. In view of this the cells and the pipes must be so formed that'the whole of the air can escape. Whenl such a waterfilled cell and outflow pipe emerge upwards on theother side out of the pulp mixture it is necessary for the diii'erence in pressure'due to the suction to be maintained as long as the free end of the outflow pipe is below the level of the water within'the cylindrical sieve, that 90 is to say until the layer of pulp has risen out of the ulp mixture. If the layer is not too thick tlzie air can then be drawn by suct/ion through it. The air will' however not penetrate through the layer of pulp before the lat-l ter has attained a certain degree of dryness anduntil this degree of dryness has been reached there will consequently be a partial vacuum in the cell which is greater than the difference in pressure between the external m" and internal liquid level and which corresponds tov the 'diierence in height between the cell in question and the required level in the interior of the sieve. When the outfiow pipe has reached a point above the water level in the interior of the cylindrical sieve .any Water present in the cell and inthe outow pipe will low out causing the suction to ceaseand the layer of pulp will then be in a position in which it can be removed in any known manner and be conveyed as stated above to a conveying device.

As, in accordance with the present invention, the layer of pulp adheres more rmly to the cylinder so that it can be raised out of the pulp mixture in a more or less vertical position, it is possible to work with a lower level of pulp mixture so that there will'be a larger portion of the sieveabove it, thus increasing the time for dewatering the pulp. The upper part of the cylinder will then provide more space for several pressing members, such for instance as dandy rollers, pressing rollers or a pressing felt which are arranged and used in a known manner.

What I claim, is: 1. A. rotary straining device for dewater- A ing librous pulp material by a dierence in pressure caused by the level of the pulp mix? Y ture outside the device being higher-,than the level of the outlowing water on the inside of the device, comprising means for maintain ing the difference in pressure until the layer of pulp adhering to the outside of the device layer o'f pulp infront ofthe corresponding y cell has risen out ofthe pulp mixture, Whereby the draining of the pipe and its associated cell causes air to be drawn through said layer ofpulp.

` In testimony whereof I'havev signed my name to this specification.

JOHN STRINDLUND.

has risen above the level of the pulp mixture outside the device, as and for the purpose set forth.

2. A rotary straining device for -dewatering ibrous material by a diilerence in pressurecaused by the level of the pulp mixture outside the device being higher than the level of the outflowing water on the inside of the device, comprising a rotary cylindrical sieve,

a pervious covering for the cylindrical sieve, a plurality of cells under the said pervious covering, an outflow pipe communicating with each cell, which pipe is bent backwards -in relation to the direction of rotation of the sieve and has its outflow end immersed in the water in the cylinder until thelayer of pulp on the pervious covering of the cylinder has risen out of the pulp mixture outside the cyl? rality of cells under the said pervious covering an outflow pipe communicating with each cell which pipe is bent backwards in relation to the direction of rotation of the sieve and having its outflow end: adapted to be immersed 

